1. Field of the Invention
The present invention generally relates to a method and a system for establishing communication between a plurality of remote units and a central location in a television transmission system and, more particularly, to a method and apparatus for transferring information such as billing information and viewing statistics from decoder units to a central location in a satellite television transmission system.
2. Description of the Relevant Art
For the purposes of the following discussion and this invention, the term "subscriber" means one who receives a television service. The "subscriber" could thus be an individual consumer with a decoder in his own home, or could be a system operator such as a local cable TV operator, or a small network operator such as a hotel/motel operator with a central decoder for all televisions in the hotel or motel. In addition, the "subscriber" could be an industrial user, as described in U.S. Pat. No. 4,866,770 assigned to the same assignee as the present application and incorporated herein by reference.
For the purposes of this invention, a network is defined as a program source (such as a pay television provider), an encoder (sometimes called a "head end"), a transmission means (satellite, cable, radio wave, etc.) and a series of decoders used by the subscribers. A system is defined as a program source, an encoder, a transmission means, and a single receiving decoder. The system model is used to describe how an individual decoder in a network interacts with the encoder.
FIG. 1 shows a prior art conditional-access system for satellite transmission. In encoder 101, the source program information 102 which comprises video signals, audio signals, and data is scrambled in program scrambler 103 using a key from key memory 104. The scrambling techniques used may be any such techniques which are well known in the art. The key can be a signal or code number used in the scrambling process which is also required to "unlock" or descramble the program in program descrambler 108 in decoder 106. In practice, one key can be used (single layer encryption) or more than one key (not shown). The key is usually changed with time (i.e.--monthly) to discourage piracy. The scrambled programs and the key are transmitted through satellite link 105, and received by conditional-access decoder 106. Decoder 106 recovers the key from the received signal, stores it in key memory 107 and applies it to program descrambler 108 which descrambles the scrambled program received over satellite link 105, and outputs unscrambled program 109.
Specific details of the features of a prior art conditional access system may be found in commonly assigned U.S. Pat. No. 4,890,319, incorporated herein by reference.
Such a system may allow for pay-per-view (PPV) and/or impulse pay-per-view (IPPV) programming. Pay-per-view programming is defined here as any programming where the subscriber can request authorization to watch a particular program. In many pay television systems, pay-per-view programming is used for sporting events (boxing, wrestling, etc.) or concerts which are not transmitted on a regular basis. A subscriber wishing to view the event must receive authorization in the form of a special descrambler mechanism, or in the form of a special code transmitted or input to the subscriber's decoder. A subscriber may, for example, receive authorization by telephoning a representative of the system operator who authorizes the subscriber by transmitting the special code to the subscriber's decoder.
Impulse pay-per-view programming is one type of pay-per-view programming. Impulse pay-per-view is a particularly attractive feature since it allows a subscriber to authorize his or her decoder to view pay-per-view programming without requiring the immediate intervention of the system operator. For example, the subscriber may control his decoder to permit viewing of a particular program by means of keypad sequence for effecting authorization. Billing information including, for example, a program ID and the time and date of purchase, is then stored in non-volatile memory of the decoder. Periodically, this billing information is transferred, for example over the public switched telephone network, to a billing computer of the system operator. The subscriber is then billed on a regular basis, e.g. monthly, for his or her purchases.
Since the billing information represents revenue to the system operator, it is important that this information be transferred in an efficient manner over a reasonable time period. The prior art contains a number of techniques for controlling the transfer of data from a plurality of remote terminals to a central location.
U.S. Pat. Nos. 4,241,237 and 4,455,453 to Paraskevakos et al. disclose remote meter reading systems where each of a number of remote units initiate callback at predetermined intervals to a central facility for billing and monitoring purposes. A central complex provides a digital instruction to each remote unit upon the completion of its data transfer. The instruction includes data to control the next scheduled callback time.
U.S. Pat. No. 4,584,602 to Nakagawa discloses a data collecting system and method which are capable of collecting television audience rating data. A marker signal initiates the callback and after waiting a predetermined time necessary for other terminal units to transmit their data, each terminal unit automatically dials a predetermined telephone number in order to transmit requested viewing data.
U.S. Pat. No. 4,696,029 to Cohen controls the initiation of voting calls through regulation of the visual stimuli which trigger the calls. A control center monitors polling call traffic at a plurality of central offices until it determines that the traffic being generated has reached a level which is not within the traffic-handling capability of the central office switching machines. The control center then sends messages which cause character generators at local affiliates to reduce the frequency and/or duration of the visual stimuli until the traffic generated has dropped to a level which is within the traffic handling capabilities of the central office.
U.S. Pat. No. 4,528,663 to Citta discloses a subscriber upstream communication technique for use in two-way CATV system. In accordance with the technique, the transmission window size is initially increased until a maximum window length is achieved and then the window size is decreased in response to a selected number of further transmission attempts. The transmission window is decreasing in size following the peak load to enhance the overall speed of the system.
PCT 89/10670 of Naddor et al., assigned to the assignee of the present application, discloses a callback technique in which a callback period is dynamically adjusted to promote efficient use of the telephone network. An initial guess is made to determine an initial callback period. Based on the number of calls received at the cable television headend, the length of the callback period is dynamically increased and/or decreased to control the callback rate.
While these and other systems are effective to varying degrees, they become less effective where the decoders are part of television systems servicing large geographical areas, e.g., the United States. For example, a satellite television system may include up to two million decoders. The need remains for a technique for establishing communication with such decoders in an efficient manner to, for example, gather billing information therefrom.